Consider using rvalue friend function in FileMappedResizableDirectMemory::Close()

**Location:** cpp/Platform.Memory/FileMappedResizableDirectMemory.h:66

**Current code:**
```cpp
// TODO: maybe use rvalue friend function
public: void Close()
{

}
```

**Issue:**
The Close() method is currently empty and there's a suggestion to consider using an rvalue friend function instead of the current approach.

**Suggestion:**
Evaluate whether using an rvalue friend function would be more appropriate for this use case and implement if beneficial.

Start with cpp/Platform.Memory/FileMappedResizableDirectMemory.h:66 and inspect the empty Close() method and its surrounding class context. Determine whether an rvalue friend function is appropriate for this use case, then verify that the resulting design and behavior match the intended resource-closing responsibility.

Written by the indexing model from the issue text.